Known in the art are aeration systems (cf. U.S. Pat. Nos. 3,461,674; Cl. 405-74, published Jan. 20, 1967; and 3,893,924; Cl. 210-220, published Oct. 19, 1973) designed to aerate water basins and comprising arranged essentially at the bottom of the basin a plurality of perforated pipes through which an air-water mixture is ejected. The air-water mixture is fed into the pipes under a pressure substantially exceeding the pressure in the bottom portion of the water basin. This is afforded either by an air-water mixing device (cf. U.S. Pat. No. 3,461,674) into which air and water are supplied by an air compressor and water pump respectively, or by an air-liquid jet aerator (cf. U.S. Pat. No. 3,893,924) wherein atmospheric air is entrained into a water jet produced by a pump.
However, both these systems require an outside power source to drive the air compressor and water pump in order to force the atmospheric air into the bottom layers of the basin being aerated. By virtue of the intermittent mode of operation of these systems, the amount of power consumed to operate them for a given period of time, such as one year, becomes quite substantial. Besides, the aforementioned systems lack structural features enabling them to be also used as dam spillways.
There is known a dam spillway (cf. USSR Inventor's Certificate No. 348,678; Cl. E 02 B 8/06, published Aug. 23, 1972) wherein the velocity head of the spilled water is used to entrain air thereinto, the head being the result of overfall transformation between a forebay and an afterbay. Incorporated into the above spillway system are outlets of conduits communicating with the atmosphere and layed essentially below the spillway surface, the air being entrained into the water flow by virtue of an underpressure produced by the mass of water moving along the spillway surface. As a result of utilizing the kinetic energy of the overflow water, this system not only eliminates damage to the spillway surface but provides aeration of the water flow, which acts to enhance the saturation thereof with oxygen. However, because this known system is an open spillway system, static pressure in the flow is close to atmospheric and the underpressure produced in the outlets of the air supplying conduits is negligible; consumption of the atmospheric air entrained into the water flow is low thereby resulting in poor utilization of the kinetic energy of the falling water.
Further known is a dam spillway system designed to effect a passage of water from a holding basin through the dam to a downstream (cf. USSR Inventor's Certificate No. 340,735; Cl. E 02 B 7/00, published June 6, 1972) comprising a means for compressing the atmospheric air by a flow of passing water. Kinetic energy of the water flow is used here more efficiently, since this spillway system features a water conduit defined by a vertically disposed mixing chamber communicating with the atmosphere and a horizontally positioned diffuser, which conduit is a means for compressing the atmospheric air. In the course of the overflow, the falling water acts to entrain into the mixing chamber the atmospheric air via the conduit thereof communicating with the atmosphere. As a result, part of the kinetic energy of the falling water is transmitted to the thus entrained air. Inasmuch as the whole of the water flow is envolved in air trapping, the amount of air thus trapped is sufficient to form an air-water mixture at the outlet of the mixing chamber. The falling water energy is further transmitted to the entrained air in the diffuser wherein the air-water mixture is subjected to a breaking action resulting in that the pressure of the mixture and, consequently, the air contained therein exceeds that of the atmosphere. This allows to force the air contained in the air-water mixture to a certain depth of the downstream. The air bubbles of the air-water mixture tend to float upwards carrying therewith to the surface of the downstream floatable solids. Therefore, by virtue of utilizing the kinetic energy of the falling water this spillway system provides the compression of air by water, aeration thereof and therefore saturation with oxygen.
However, this system suffers from a disadvantage in that the effect of formation of the air-water mixture and floatation of the floatable pollutants by the air bubbles is not used for cleaning the downstream water.